1. Field of the Invention
The present invention relates generally to an improved lubrication system for an internal combustion engine and, more particularly, for a lubrication system that advantageously utilizes the pulsating pressure variations within certain sections of the crankcase to draw lubricating fluid through main bearing regions that would otherwise be difficult to lubricate.
2. Description of the Prior Art
Many portions of an internal combustion engine require lubrication to avoid damage caused by friction at various interfaces between stationary and moving components. For example, oil in provided in the interface region between the cylinder walls of the engine and the outer surfaces of the pistons. Furthermore, various regions of the crankshaft require support by bearings which, in turn, require adequate lubrication.
Internal combustion engines that are used in outboard motors present particular challenges to a lubrication system. Since the internal combustion engine is operated in a vertical configuration, with the crankshaft rotating about a vertical axis and with the pistons and cylinders disposed in a vertical arrangement, it is common to take advantage of the force of gravity to distribute lubricant throughout the engine. In addition to the use of gravity, it is also well known to those skilled in the art of outboard motor design to utilize differential pressure to distribute oil from one region of an engine to another. As an example, oil which has drained to the bottom portion of an engine region is commonly transmitted to a top bearing zone through the use of differential pressure.
U.S. Pat. No. 5,632,241, which issued to Binzersiel on May 27, 1997, discloses an oil lubricating system for a two-stroke internal combustion engine. The lubricant supply system for the internal combustion engine includes first and second adjacently located and substantially sealed crankcase chambers which alternately experience high and low pressure conditions which are out of phase with respect to the occurrence thereof. First and second oil supply passages communicate with the first and second crankcase chambers. An oil supply circuit includes an oil supply chamber that is adapted to contain oil and have therein a formation including a recess isolated from the oil supply chamber in communicating with the first and second oil supply passages. A metering rod includes an indentation and is supported in the oil supply chamber for movement of the formation between a first position wherein the indentation is located in the oil chamber and a second position wherein the indentation is located in the formation in communication with the recess. When in the first position, the formation affords the filling of the indentation with oil. The system also includes a mechanism for defecting movement of the oil metering rod between the first and second positions.
U.S. Pat. No. 4,599,979, which issued to Breckenfeld et al, on Jul. 15, 1986, describes an upper crankshaft bearing lubrication system for a two cycle engine. The engine has a sump in a lower portion of the crankcase for collecting engine fuel drains and a crankshaft bearing lubrication system includes a first conduit means that is connecting the upper crankshaft bearing in communication with the engine intake manifold. It also includes a second conduit means connecting the upper crankshaft bearing in liquid communication with the sump and has an intermediate portion or reservoir. A third conduit means connects the crankcase in communication with the reservoir. A first check valve is located between the sump and the reservoir permitting fuel drains to flow from the sump upwardly toward the upper crankshaft bearing in response to a suction created in response to the low pressure or vacuum in the intake manifold and prevents backflow from the reservoir to the sump. A second check valve is located between the crankcase and the reservoir and permits flow from the crankcase into the reservoir to pump drains from the reservoir to the upper crankshaft bearing when a high pressure condition exists in the crankcase and for preventing a backflow from the reservoir to the crankcase when a low pressure exists in the crankcase.
U.S. Pat. No. 5,524,581, which issued to Rush et al, on Jun. 11, 1996, discloses an outboard motor with an improved lubrication system. The engine comprises a cylinder block which defines a cylinder, a crankshaft bearing supported in part by the cylinder block, a crankshaft which is rotatably supported by the crankshaft bearing, a piston slidably housed in the cylinder, a connecting rod having one end connected to the piston and having an opposite end connected to the crankshaft, a cylinder head mounted on the cylinder block, a camshaft at least partially supported by the cylinder head for rotation relative thereto, an oil pump with an outlet, a first oil conduit communicating between the oil pump outlet and the crankshaft bearing, and an oil filter communicating with the first oil conduit for filtering oil only in the first oil conduit. In addition, it comprises a second oil conduit that communicates between the oil pump outlet and the camshaft. Oil in the second oil conduit is unfiltered between the pump outlet and the camshaft.
U.S. Pat. 4,820,212, which issued to McElroy et al, on Apr. 11, 1989, describes a marine propulsion device bearing lubrication system. The marine propulsion device comprises an engine, a lower unit adapted to be mounted on the transom of a boat for pivotal movement relative thereto about a generally vertical steering axis with the lower unit including a lower gearcase having a lubricant therein. It also includes a propeller that is rotatably supported by the lower gearcase. A generally vertical driveshaft is rotatably supported in the lower unit and includes an upper end which is driven by the engine. A lower end is drivingly connected to the propeller. An axial bore extends upwardly from the lower end and defines a sleeve portion of the driveshaft. An aperture extends radially through the sleeve portion and internal threads within the axial bore assist in pumping lubricant from the lower gearcase upwardly through the axial bore to the aperture so that the lubricant can flow outwardly through the aperture.
U.S. Pat. No. 4,121,551, which issued to Turner on Oct. 24, 1978, discloses a drain recycle system for a two cycle engine. The internal combustion engine includes a cylinder having a fuel intake port, an exhaust port, and an inlet port located intermediate the intake and exhaust ports. It also includes a piston that is reciprocally mounted in the cylinder and a crankcase which has a drains collection area. A conduit means connects a liquid communication with the drains collecting area and with the inlet port. The drains are recycled or recirculated from the drains collecting area to the cylinder for ultimate combustion therein in response to the cyclical variation of pressure in the crankcase and in the cylinder. In a particular embodiment, the conduit means includes a first conduit which is connected in liquid communication with the drains collecting area and with an upper bearing rotatably supporting the engine crankshaft and a second conduit which is connected in liquid communication with the upper bearing and with the inlet port so that the recirculating drains contact and lubricate the upper bearing en route to the cylinder.
It has been determined that in particular engine designs, certain areas of the crankshaft and support bearings may not be properly lubricated in some circumstances. Because of the location of various seals and because of the cyclical pressure changes of the crankcase regions, certain outboard motors are not properly lubricated if the lubrication system relies solely on gravity to cause the lubricant to flow through the engine. In particular, the two center main bearings of a 6 cylinder two-cycle internal combustion engine do not always receive an adequate supply of lubricant if the forces of gravity are relied upon solely to transmit the lubricant to the center main bearings.
In view of the above, it would be significantly beneficial if a means could be provided to facilitate the flow of lubricant to all critical regions of an internal combustion engine, even when the particular design of the engine block and crankshaft do not always allow gravity to cause lubricant to flow into all portions of the engine and crankshaft region that require lubrication.